This paper deals with the stability problem of three stator current error-based estimators of the induction motor speed, especially in the regenerating operation mode. The stability of the Adaptive Full-order Observer (AFO) and two Model Reference Adaptive System (MRAS) based on stator current error (MRASCC and MRASCV) is briefly analysed and the stability boarders are determined and compared. It is shown, that MRASCV speed estimator is stable in the whole operation range including the regenerating mode. The stability enhancement method for AFO and MRASCC estimators is described and solution for their stability improvement is proposed. Torque-speed characteristics of the analysed MRAS-type estimators in a wide range of drive speed and load torque changes are given as well as the behaviour of estimators during transients is compared. The theoretical analysis and simulation test results are validated by experimental tests.